1. Field of this Invention
The present invention relates to a process for producing ceramic, metal or mixed metal-ceramic catalyst supports or catalyst systems with a given macroporosity and a microporisity which can be influenced by the production conditions.
2. Prior Art
The choice of starting materials is determined by the application range of the catalyst or catalyst systems in regard to the reaction temperature, gaseous atmosphere and nature of the catalyst material employed.
In the case of a catalyst system, it is advantageous for a maximum gas-solid material contact surface to be available --.sub.which as far as possible does not change during the course of the reaction. In this respect, it can be advantageous to use a catalyst support consisting of a material which is stable at the reaction temperature and does not form sinter. The actual catalyst material can be applied to this support by various processes. However, it is also possible to produce this kind of framework material directly from the catalyst material, provided the catalyst material is stable under reaction conditions and provided this scheme is economically feasible. It is also possible to add a certain amount of catalyst material in finely distribued form to a material inactive as a catalyst and to produce the support material and apply the catalyst material in a single operation.
Concerning the operation of this type of catalyst system it is critically important in regards to a uniform perfusion of the catalyst material for there to be complete utilization of the entire catalyst surface and a uniform period of dwell (residence or pass through time) of the reaction gases in the catalyst system, a uniform pore distribution in the catalyst system, a regular pore size and defined interconnection openings between the pores.
According to the known processes, porous, ceramic materials may be produced by skimming off or burning out specific auxiliary materials which were mixed with the crude mass. However, in the case of the materials produced according to these processes it has only been possible to obtain an irregular pore distribution and size and it is largely left to chance as to whether a junction between the individual pores is obtained. Apart from the open pores, closed pores are also produced which are ineffective when the material is used as a catalyst or a catalyst support. Apart from this, in the case of materials of this nature, irregular periods of dwell of the reaction gases in the different parts of the catalyst system occur which can lead to local overheating as a result of different reaction speeds.